Jon Elson wrote:
> Sebastian Kuzminsky wrote:
>> Jon Elson wrote:
>>> OK, same problem as my PPMC line, then. But, 1 KHz isn't fast
>>> enough? Or, does handling the Mesa's 72 I/O points take a lot
>>> longer than my 24?
>>
>> I haven't done speed tests of the 7i43 with hostmot2 for a while, but i
>> think low ones of KHz update rates are reasonable. Say 1-4 KHz or so.
>> That's for reading all the encoders, stepgens, and gpios, and writing
>> all the pwmgens, stepgens, and gpios.
>
> OK, that is reasonably close to what I'm getting, considering
> the greater I/O points. I can run up to 10 KHz with one of my
> UPC or USC boards with on-motherboard PP on a 600 MHz pentium
> II. I can go to 5 KHz with 2 UPC's, so that's 8 axes 16 digital
> outs and 31 digital ins, on the same machine. I can probably go
> to 10 KHz with 2 boards with a PCI parallel port and a little
> faster CPU.
That 1-4 KHz figure is an old measurement I remembered for 4-channel
servo control (on the 7i43 board): read 4 encoder counts (counted by the
FPGA), do 4-channel pid in emc2, then write 4 PWMs.
I ran some tests tonight on my development machine, a single-processor
Celeron running at 2.6 GHz. Please remember that the driver is still
under development and basically not optimized at all: these figures may
change in the future.
The values for "time" reported below is the average time taken by the
function (measurement is approximate average of 10 or so random
samples). The values for "tmax" is the longest time taken by the
function after a few minutes of runtime. All times in microseconds.
7i43:
pet_watchdog (or else it bites) time=47, tmax=57
read (4 encoders, 4 steppers, 48 gpio inputs) time=245, tmax=260
write (4 pwmgens, 4 steppers, 48 gpio outputs) time=235, tmax=637
read_gpio (48 gpio inputs) time=37, tmax=49
write_gpio (48 gpio outputs) time=35, tmax=46
So if we're just talking about reading & writing gpios, you can do that
at about 7 KHz and still have 50% of your CPU time left over for other
things. Or 2 KHz if you want the watchdog enabled.
If I disable the steppers on the 7i43 (with config="num_steppers=0") and
run it with 4 servo channels (and 24 accessible GPIOs), I get these figures:
read time=191, tmax=203
write time=190, tmax=239
That's about 1 KHz.
And just for fun, the numbers for the 5i20:
pet_watchdog (or else it bites) time=6, tmax=13
read (8 encoders, 4 steppers, 72 gpio inputs) time=52, tmax=62
write (8 pwmgens, 4 steppers, 72 gpio outputs) time=15, tmax=27
read_gpio (72 gpio inputs) time=13, tmax=42
write_gpio (72 gpio outputs) time=5, tmax=12
--
Sebastian Kuzminsky
Cryogenic travel has improved since then... I woke screaming in a
translucent box. “There, there,” said the box. “Everything will be all
right. Have some coffee.” -- Ken Macleod, "Who's afraid of Wolf 359"
<http://outofthiseos.typepad.com/blog/files/KenMacleodWhosAfraidofWolf359.htm>
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